In an integrated circuit device which includes a plurality of integrated circuits, the difference in the power supply voltage level between the integrated circuits may cause a problem. To address this, the outputs of the power supply circuits integrated in the integrated circuits are often electrically connected to each other. In the case that a display panel (for example, a liquid crystal display panel) is driven by a plurality of driver ICs, for example, a difference may be generated between images displayed in the portions driven by the different driver ICs in the display panel, if the boosted power supply voltages generated by boosting power supplies of the driver ICs are different. One approach to solve this problem is to connect the outputs of the boosting power supplies in the driver ICs to a common power supply line for generating the same boosting power supply voltage in the plurality of driver ICs. The boosting power supply voltage thus generated is used to drive the display panel.
One possible problem is that, in the configuration in which the outputs of the power supply circuits integrated in the integrated circuits are electrically connected to each other, an overcurrent may be generated depending on the configurations and operations of the power supply circuits, when the plurality of power supply circuits are activated at different timings. Such a problem is the case with a configuration in which the outputs of the two power supply circuits are electrically connected to each other through the power supply line, each of the two power supply circuits having the output connected to ground when the operation thereof is stopped. More specifically, when one of the power supply circuits is already activated and the other of the power supply circuits is not activated yet, an overcurrent may flow to ground from the power supply line in the other power supply circuit. The generation of the overcurrent is desired to be avoided.